Frequently Asked Questions
How accurate is this calculator?
The calculator provides estimates based on standard UK board sizes, joist spacings, and industry waste factors. Actual quantities may vary depending on your specific boards, cutting accuracy, and site conditions. Always order 10–15% extra.
Is my data private?
Yes. All calculations run entirely in your browser. We never send your dimensions, costs, or project details to any server. Saved inputs are stored in your browser's localStorage and never leave your device.
Is this professional advice?
No. This calculator provides estimates for planning purposes only. It is not a substitute for professional advice. Always consult a qualified builder or structural engineer for raised decks, load-bearing structures, or any project you are unsure about.
When was the calculator last updated?
The calculator and pricing data were last updated in January 2025. We review prices and material specifications regularly to keep estimates current, but prices change frequently — always confirm with your supplier.
Can I export my results?
Yes. After calculating, click the 'Export PDF' button to download a print-ready PDF containing your input summary, full materials list, cost breakdown, and timestamp. The PDF is formatted for easy reading and sharing.
How do I report an error or bug?
Use our contact form at /contact and select 'Report a bug or error' from the subject dropdown. Include as much detail as possible — the inputs you used, the expected result, and what you actually saw.
What waste percentage should I use?
Standard parallel layouts: 10%. Diagonal layouts: 15%. Herringbone patterns: 20%. These are conservative estimates — experienced builders may achieve less waste, while first-time DIYers should consider adding an extra 5%.
Does the calculator include labour costs?
No. The calculator estimates material costs only. Professional installation typically costs £40–60 per square metre on top of materials. DIY builds save this entire cost.
Can I calculate for composite and timber?
Yes. Select your board material from the dropdown — the calculator adjusts board width, available lengths, pricing, and recommended joist spacing automatically for each material type.
Why are the prices different from my local supplier?
Our prices are estimates based on typical UK supplier pricing averaged across major retailers and timber yards. Actual prices vary by region, supplier, stock levels, and whether you buy individual boards or full packs. Always get quotes from your preferred supplier.
Can I save my calculation for later?
Yes. Click the 'Save' button to store your inputs in your browser. When you return to the calculator, your previous values will be automatically restored. This uses localStorage — clearing your browser data will remove saved calculations.
What is the difference between Full Build and Cost Only modes?
Full Build calculates every component: boards, joists, bearers, posts, screws, and weed membrane with quantities and costs. Cost Only shows the same total cost but focuses on the price breakdown rather than the itemised shopping list.